<!DOCTYPE html>
<html lang="zh-CN">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>封装一个jQuery</title>
</head>

<body>
  <div class="test">
    测试
    <div class="child">child1</div>
    <div class="child">child2</div>
    <div class="child">child3</div>
  </div>
  <div class="test">
    测试
    <div class="child1">child1</div>
    <div class="child">child2</div>
  </div>
  <div id="main">
    <div class="test">
      测试
      <div class="child">child1</div>
    </div>
  </div>
</body>
<script src="./jquery.js"></script>
<script src="./main.js"></script>

</html>